Borexino is located in the Hall C of Laboratori Nazionali Gran Sasso (LNGS-INFN) [1]}. The detector is made of concentric shells with increasing radiopurity (see e.g. Ref. [2]}): the innermost core, enclosed in a 125 \(\mu \) m thick ultra-pure nylon vessel of radius 4.25 m, is made of about 280 tons of liquid scintillator (1,2,4-Trimethylbenzene with 1.5 g/l of PPO wavelength shifter). The active core is contained in a stainless steel sphere (SSS) filled up with \(\sim 1000\)  tons of buffer liquid (1,2,4-Trimethylbenzene with DMP quencher), whose internal surface is instrumented with more than 2000 PMTs for detecting the scintillation light. Finally, the SSS is located inside a 2000 tonne water Cherenkov detector, equipped with about 200 PMTs.
Thanks to an intense calibration campaign carried out in 2010, the Borexino detector is able to reconstruct the event position with an accuracy of \(\sim 10\)  cm (at 1 MeV) and with energy resolution of about \(\sigma (E) / E = 5\%/\sqrt{(}E/[MeV])\)  [3]}.
